The present invention is directed to a method for adjusting coupling optics for coupling light into a waveguide, which coupling optics are provided at the end of an optical waveguide to couple light from a semiconductor laser. The method includes establishing the longitudinal spacing along the optical axis of the waveguide between the end of the waveguide having the coupling optics and the semiconductor laser and adjusting the position of the waveguide and coupling optics relative to the semiconductor laser in an x and y direction which lie in a plane extending perpendicular to the optical axis to obtain the optimum and maximum value of light coupling between the laser and waveguide. The invention is also directed to an apparatus used for the implementation of the method.
Given the construction of transmission modules with monomode fibers, the coupling optics are composed of a fiber taper with a refractive lens and must be adjusted and subsequently fitted with reference to the laser diode in a longitudinal direction z, which is along the optical axis of the waveguide. In addition, the monomode fiber and coupling optics must be adjusted relative to the laser diode in two mutually orthogonal directions x and y which lie in a plane which is perpendicular to the longitudinal direction z.
Given all known module construction technologies with coupling optics which have a lens at the end of the fiber, the fiber is adjusted to a maximum coupling efficiency and is then fixed in this position. The adjustment to the maximum coupling efficiency occurs by means of measuring a light power coupled via the coupling optics at the end of the fiber into the fiber itself. Since, in practice, the adjustment in longitudinal direction z is not independent of the adjustments in the transverse directions x or y, the optimum fiber position can only be found step-by-step by means of alternately adjusting in both the longitudinal direction and adjustment in the transverse directions. Thus, the fixing is relatively tedious and time-consuming.
The fixing of the fiber usually occurs by means of soldering for reasons of long-time stability. In order to be able to operate an InGaAsP/InP laser, with the temperatures occurring for soldering, the laser would have to be cooled during the soldering process or be constructed to be thermally insulated from the solder location.